This invention is related to blocked organic acids used as a catalyst in coating compositions and in particular to amino methyl proponal blocked aromatic sulfonic acids.
The use of aromatic sulfonic acids as catalysts for thermosetting coating compositions containing amino resin crosslinking agents such as melamine formaldehyde resins, alkylated melamine formaldehyde resins or urea formaldehyde resins are well known in the art as shown in Gallacher U.S. Pat. Nos. 4,075,176 issued Feb. 21, 1978 and in Gallacher 4,083,830. The application "pot life" i.e., the time during which the coating can be applied, for example by spraying, of such coating compositions containing aromatic sulfonic acids catalysts was relatively short. To increase pot life, blocked aromatic sulfonic acid catalysts were developed using an oxa-azacyclopetane compound as shown in Calbo U.S. Pat. Nos. 4,200,729 issued Apr. 29, 1980 and in Calbo 4,251,665, issued Feb. 17, 1981. These blocked catalyst unblocked during baking of the coating thereby providing free acid which catalyzes the curing reaction.
These blocked aromatic sulfonic acid catalysts are not as stable as desired by the automotive paint industry and are relatively expensive. There is a need for a blocked aromatic acid catalyst that is inexpensive and is stable for extended periods of time in storage and in the coating composition to which it has been added.